Direction finder



May 18, 1948. E. D. BLODGETT ETAL DIRECTION FINDER Filed March 30, 1945 2 Sheets-Sheet 1 INVENTORS @lwar-JRBW I y 1943' E. D. BLODGETT EI'AL 2,441,658

DIRECTION FINDER Filed March 30 1945 2 Sheets-Sheet 2 Patented May 18, 1948 DIRECTION FINDER.

Edward D. Blodgett, Haddoniield, N. J., and

Donald S. Bond,

Radio Corporation of of Delaware Philadelphia, Pa., assignors to America, a corporation Application March 30, 1945, Serial No. 585,672

1 9 Claims.

This invention relates to radio direction finders, and more particularly to improvements in the art of bearing indication with direction finder systems.

The principal object of the instant invention is to provide improved methods of and means for indicating directional information on the fluorescent screen of a cathode ray tube.

The invention will be described with reference to the accompanying drawing, of which Figure 1 is a schematic circuit diagram of a radio direction finder embodying the present invention,

Figure 2 is a polar graph of directive patterns of the antenna of the system of Figure 1,

Figure 3 is a view of a typical cathode ray in-v dication produced under certain conditions of operation of the system of Figure 1, and

Figures 4 through 8 are views of other typical indications produced under various conditions of operation of the system of Figure 1.

Refer to Figure l. A directive antenna 1 is arranged for rotation about a vertical axis by means of a shaft 3, schematically indicated by dash line. In the present illustration, the anterms, I comprises four vertical dipoles 5, 1, 9 and H, equally spaced laterally of a reflector screen I 3. The outer dipoles and II are connected differentially with respect to each other to a transmission line 15. The inner dipoles 1 and 9 are connected in parallel aiding relationship with each other to a transmission line l1.

A reversing switch I9 is included in the line I5, which extends from the switch l9 to a radio receiver 2|. The switch 19 is arranged to be periodically actuated by a cam and follower arrangement 23, driven by a motor 25. The motor is energized from a source 21, through a switch 29. A switch 3| is provided in the line I1, which extends thence to a 90 phase shifter 33. The output of the phase shifter 33 is connected to the receiver 2f.

The output circuit of the receiver 21 is coupled through a transformer 35 to a rectifier 31. .One output terminal of the rectifier 31 is grounded, and the other is connected to the movable contact of a double-throw switch 39. The stationary contacts are bridged by a capacitor network M, and are connected to the terminals of a zerocenter miliiammeter 43. The meter 43 is a conventional left-right indicator. The double-throw switch 39 is mechanically coupled to the antenna, switch l9, for operation in synchronism therewith by the switching motor 25.

The operation of the system thus far described is substantially the same as that of a conven- 2 tional radio compass of the L-R indicator type. The switch 29 is closed to energize the motor 25, and the switch 3| is closed, connecting the center antennas 1 and 9 to the phase shifter 33. When the switch 19 is in its upper position, the dipoles 5 and II are connected to the receiver 2| in such polarities that their output, combined with the phase-shifted output of the center antennas 1 and 9, provides a directive pattern with its axis of maximum response at an angle to the left of the center line of the antenna. Referring to Figure 2, the directive pattern under this condition is represented by the solid line curve 45, where t the line A-A indicates the plane of the reflector I3. Similarly, when the switch I9 is in its lower position, the directive pattern is shifted to the right, as shown by the dash line curve 41 of 4 Figure 2.

The amplitude of the output of the receiver 2i is substantially proportional to that of the input. This output is rectified by the rectifier 31 and applied to the switch 39. When the switch 39 is in its upper position, the capacitor 42 is charged to a voltage proportional to the amplitude of the signal picked up by the antenna i with the left-hand directive pattern 45. When the switch 39 is in its lower position, the capacitor 40 is charged similarly to a voltage corresponding to the signal picked up with the right hand pattern 41.

The charges on the two capacitors 40 and 42 are substantially equalized during each cycle of switch operation, by current flowing through the meter 43. The direction of flow of the equalizing current, and hence the direction of deflection of the meter 43, is in accordance with the angle of arrival of the signal at the antenna I. Thus, if the signal arrives along a line to the left of the equisignal axis 00, the meter 43 is deflected to the left,-and vice versa. If the signal arrives along the line 00, the output of the receiver 2! does not change with the antenna switching, and the meter 43 shows no deflection.

An azimuth indicator 49 is provided on the shaft 3. When the shaft 3 is rotated to a position such that the indication of the meter 43 is zero or centered and shows a bearing reading, the indicator 49 shows the angular position of the shaft 3, which corresponds directly to the direction of wave arrival. The shaft 3 may be rotated by means of a handwheel (not shown) or by means of an electric motor 5| coupled to the shaft and provided with a source 53.

The source 53 is connected to the field of the motor 5| through a switch '55, and to the armare through a double-throw switch 51. When e switch 51 is thrown to its left hand position, e motor is energized to drive the shaft 3 ntinuously for "searching and also to provide ntinuous direct indication of azimuth on the reen of a cathode ray tube, as described hereafter. when the switch 51 is thrown to its right hand isition, the armature of the motor 5| is conacted to the source 53 through the contacts 50 a polarized relay I. The contacts 5! are conacted as a reversing switch, so that the direcon of rotation of the motor 5| depends upon 1e polarity of the voltage applied to the actuting winding of the relay 3|. This winding is annected across the meter 43. It will be clear I those skilled in the art that the last-mentioned Jnnection may include an amplifier, or that the elay 5| itself may be an electron dischargetube lrcuit of known type. r

The operation or the system with the switch 1 in its right hand position is substantially the ame as that of an automatic self orienting radio ompass. If the signal arrives along a line to he left of the equisignal axis of the antenna, the elay 8| is energized in the proper polarity to :ause the motor 5| to rotate the shaft 3, and with it the antenna I, to the left. Conversely, he arrival of a signal from a direction to the 'ight of the equisignal axis will cause rotation of he antenna to the right. Thus the antenna will we driven to a position such that the equisignal iXlS coincides with the line of signal arrival, whereupon the relay 6| will be deenergized and the motor 5| disconnected from its source 53. The direction of arrival is then indicated by the azimuth indicator 49.

The above-described automatic antenna positioning means is given merely as an illustration, and it should be understood that any other known type of servo system may be substituted forthe polarized relay arrangement shown, or the automatic positioning feature may be omitted, and the shaft 3 rotated by hand to the null position.

An adjustable voltage divider device 63 is provided on the shaft 3, with two rotatable contact members 65 and .61, spaced apart angularly 90, and a ring-like stationary resistor element 89. The element 89 is provided with two diametrically opposite input terminals 1| and 13 respectively. The element 89 has a suitable non-uniform winding so as to give sinusoidal variation of voltage between the points 1| and 65 or 51 with rotation of the shaft 3. The terminal 1| is connected to the movable contact of the doublethrow switch 15, and the terminal 13 is connected to the movable contacts of the doublethrow switch 11. One stationary contact of the switch 15 is connected to the positive, or ungrounded terminal of the rectifier 31. The other stationary contact of the switch 15 is connected to the movable contact of a double-throw switch 19. The stationary contacts of the switch 15 are connected respectively to the terminals of the meter 43.

AD.-C. source 8| is connected to one stationary contact of the switch 11 and to ground. The other stationary contact of the switch 11 is connected to the ungrounded output terminal of the receiver 2|.

The movable contacts 55 and 61 ofthe voltage divider 53 are connected respectively to the vertical and horizontal deflection circuits of'-. a cathode ray tube'83. The tube 83 is provided a function of 0.

with the usual electronic gun and accelerating electrodes, not shown. An azimuth scale is provided on the face of the tube 33. The scale 35 may be a translucent mask or the like calibrated in degrees and arranged so that the pattern appearing on the screen may be compared in angular'position with the scale.

The operation of the above-described indicator system is as follows:

The voltage appearing between the movable taps 55 of the voltage divider l3 and the terminal 1| depends upon the angular position of the shaft 3. Assuming a voltage E to be impressed between the terminals 1| and 13, a voltage E'=E sin 0 appears between the contacts 55 and the terminals 1|, where o is the angular position of the shaft 3 with respect to a predetermined reference position. Similarly, a voltage E"=E cos 0 appears between the tap 51 and the terminal 1|. Thus if the point 1| were grounded, and the switch 11 placed in its lower position to connect the source 8| between the points 1| and 13, rotation of the shaft 3 would produce a circular trace on the screen of the cathode ray tube 83. The diameter of the trace would be directly proportional to the voltage of the source 8|.

Now if the voltage E between the points 1| and 13 is varied as the shaft 3 is rotated, the radius of the fluorescent trace will vary accordingly, producing a pattern which is not circular, but is actually a polar graph of the variation of E as The output of the rectifier 31 may be utilized in several different ways to vary E and cause characteristic patterns on the cathode ray tube.

Assume that the switch 11 is in its lower position and the switch 15 is in its left-hand position. The switch 51 is placed in its left-hand position causing the motor 5| to rotate the shaft 3 continuously. The swich 19 is closed in either position, for example to the left. The voltage E across points 1| and 13 of the voltage divider 63 now consists of the sum of the voltage of the source 8| and the voltage between one side of'the meter 43 and ground. The first component is constant, providing a circular base line on the cathode ray indication. The second component varies in magnitude according to the amplitude of the output of the receiver 2|, and has a polarity depending upon whether the signal arrives at the antenna from the left or the right'of the equisignal line.

Referring to Figure 3, the resulting pattern comprises a series of oscillations outside the base line to the left of the equisignal point and inside the base line to the right. The cross over 9| clearly indicates the equisignal point. The radial oscillations are caused by the operation of the switches |9 and 35.; If the switch 19 is thrown to its other position, a similar pattern will appear, but it will be the mirror image of the pattern of Figure 3. In either case, the position of the point 5| with respect to the scale 85 indicates the azimuth of wave arrival.

Patterns which are Symmetrical about the equlsignal point can be produced by throwing the switch 15 to its right-hand position. The output of the rectifier 31 is then added directly to the voltage of the source 8|, without going through the switch 39. The result is that the radial deflection caused by an arriving signal is in the same direction, whether the signal comes from the right or the left of the equisignal line. When "the 'output of the rectifier is of such '76 polarity as to oppose the source 8|, the deflection is inward from the circular base line. and the pattern is of the type shown in Figure s, where 38 is the equisignal point. The output of the rectifier 31 may be reversed in polarity by means of the switch 88, providing the pattern shown in Figure 5, with outward deflection to the left and right of the equisignal point 85.

Another type of symmetrical pattern may be provided by applying the output of the receiver 2i directly to the voltage divider 83, omiting the D.-C. source 8!. This is done by throwing the switch I? to its upper position and closing the switch 18. The switch i is opened. The resulting cathode ray pattern is of the type shown in Figure 8, where 87 is the equisignal point. This pattern has an envelope identical with the directive patterns of the antenna, shown in Figure 2, and presents a convenient method of checking the operation of the antenna.

Any of the above described indications may be used alone to provide direct azimuth indication. It has also been found convenient in practice to employ the direct cathode ray indication for searching a signal, and when a signal is found, to switch the system to the self-orienting operation described above.

All 01' the above described types of operation 01' the system involve lobe-switching of the antenna pattern. Another type of indication, which is useful under certain conditions, may be obtained by stopping the antenna switch and disconnecting the central antennas land 9, so that the outer antennas 5 and II operate as a, diiierentially connected spaced pair, somewhat like an elevated H Adcock array.

The switches 29 and 3| areopened, deenergizing the switch motor and disconnecting the dipoles I and 9. The switches TI and 18 are opened. The switch I! is placed in its righthand position. The switch '0 is closed, grounding the point 13 oi the voltage divider 33. The rectified output of the receiver is now applied directly across the voltage divider 83, and the radial deflection of the beam of the cathode ray tube 83 will be proportional to the signal input of the receiver. Upon rotation of the shaft 3. a pattern of the type shown in Figure 7 will appear. This is a, polar graph of the directive pattern of the difierentially connected dipoles 5 and I3. The null point 89 corresponds in position to the equisignal points occurring in the operation of the system with antenna switching. If the antenna is continuously rotated so that the entire pattern of Figure 7 is visible continuously, the signal azimuth may be determined by comparison of the pattern with the scale 85. Like the pattern of Figure 6, this indication is useful in checking the operation of the antenna system.

Another pattern, somewhat more convenient for azimuth indication, is provided by connecting the source 8| difierentially in series with the output of the rectifier 3'! across the voltage divider '83. This is done by opening the switch 80, closing the switch H in its lower position, and setting the reversing switch 3! in its upper position. The cathode ray deflection is inward from a circular base line, as described in connection with Figure 4, but is controlled in accordance with the directivity of the difierentially connected dipoles 5 and I I, rather than the switchedlobe pattern. The trace on the cathode ray tube screen is of the type shown in Figure 8, where the'point IOI represents the null of the directive pattern. The position of this point is compared with the scale I! to determine the azimuth. As in the above described methods of operation, the shaft 3 may be rotated continuously by the motor 5|. or rotated to the null point, which in this case is the angle of maximum deflection oi the cathode ray beam.

Thus the invention has been described as an improved direction finder system. including indicator means comprising a cathode ray tube and radial deflection circuits. Signals picked up by a rotatable directive antenna are received, rectified and applied to the deflection circuits to provide characteristic patterns indicating the azimuth of signal arrival,

We claim as our invention:

1. A radio direction finder including a directive antenna having substantially a sirigle-lobed responsive pattern, means cyclically-varying the direction of said pattern with respect to said antenna alternately between two overlapping positions, means including a shaft for rotating said antenna about a redetermined axis, a radio receiver connected to said antenna, a rectifier connected to said radio receiver, a cathode ray tube including a fluorescent screen, means responsive to the angular position of said shaft to deflect the cathode ray of said tube radially outward from the center of said screen in a direction corresponding to said angular position and normally to a predetermined radius, and means responsive to the output of said rectifier to increase the extent oi said radialidefiection in accordance with a predetermined function of the output or said rectifier. a

2. A radio direction finder including a directive antenna having substantially a single-lobed responsive pattern, means cyclically varying the direction of said pattem with respect to said antenna alternately between two overlapping positions, means including a shaft for rotating said antenna about a predetermined axis, a radio receiver connected to said antenna, a rectifier connected to said radio receiver, a cathode ray tube including a fluorescent screen, means responsive to the angular position of said shaft to deflect the cathode ray of-said tube radially outward from the center of said screen in a direction corresponding to said angular position and normally to a predetermined radius, and means responsive to the output of said rectifier to reduce the extent of said radial deflection in accordance with a predetermined function of the output of said rectifier.

3. A radio direction finder including a directive antenna having substantially a single-lobed responsive pattern, means cyclically varying the direction of said pattern with respect to said antenna alternately between two overlapping positions, means including a shaft for rotating said antenna about a predetermined axis. a radio receiver connected to said antenna, a rectifier connected to said radio receiver, a cathode ray tube including a fluorescent screen, meansresponsive to the angular position of said shaft to deflect the cathode ray of said tube radially outward from the center of said screen in a direction corresponding to said angular position, and means responsive to the output of said rectifier to control the extent of said radial deflection directly in accordance with the output of said rectifier.

4. A radio direction finder including a directive antenna having substantially a single-lobed responsive pattern, means including a periodic switch cyclically varying the direction of said pattern with respect to said antenna alternately between two overlapping positions, means including ashaft for rotating said antenna about a predetermined axis, a radio receiver connected to said antenna, a rectifier connected to said radio receiver, a cathode ray tube including a fluorescent screen, means responsive to the angular position of said shaft to deflect the cathode ray of said tube radially outward from the center of said screen in a direction corresponding to said angular position, and means responsive to the output of said rectifier to control the extent of said radia'l deflection in accordance with a predetermined function of the output of said rectitier, said last-mentioned means including a second periodic switch reversing the polarity of said output in synchronism with said variation in direction of said directive pattern.

5. A radio direction finder including a directive antenna, means for periodically altering the direction of maximum response of said antenna with respect to a predetermined horizontal axis thereof, means including a shaft for rotating said antenna about a vertical axis, a radio receiver connected to said antenna, a rectifier connected to said receiver, a cathode ray tube including a fluorescent screen, means responsive to the angular position of said shaft to deflect the beam of said cathode ray tube radially outward from the center of said screen in a direction corresponding to said angular position, and means responsive t the output of said rectifier to control the extent of said radial deflection as a predetermined function of said output.

6. A radio direction finder including a directive antenna, means for periodically altering the direction of maximum response of said antenna with respect to a predetermined horizontal axis thereof, means including a shaft for rotating said antenna about a vertical axis, a radio receiver connected to said antenna, a rectifier connected to said receiver, means for reversing the polarity of the output of said rectifier periodically and in synchronism with said alterations in the directivity of said antenna, a cathode ray tube including a fluorescent screen, means responsive to the angular position of said shaft to deflect the beam of said cathode ray tube radially outward from the center of said screen in a 'direction corresponding to said angular position and normally to a predetermined radius, and means responsive to the output of said polarity-r'eve'rsing means to increase the extent t said radial deflection as a predetermined function of said output.

'7. A radio direction finder including a directive antenna, means for periodically altering the direction of maximum response of said antenna with respect to a predetermined horizontal axis thereof, means including a shaft for rotating said antenna about a vertical axis, a radio receiver connected to said antenna, a rectifier connected to said receiver, means for reversing the polarity of the output of said rectifier periodically and in synchronism with said alterations in the directivity of said antenna, a cathode ray tube including a fluorescent screen, means responsive to the angular position of said shaft to deflect the beam of said cathode ray tube radially outward from the center of said screen in a direction corresponding to said angular position and normally to a predetermined radius, and means responsive to the output of said polarityreversing means to reduce the extent of said radial deflection as a predetermined function of said output.

8. A radio direction finder including a directive antenna, means for periodically altering the direction of maximum response of said antenna with respect to a predetermined axis thereof. means including a shaft for rotating said antenna about an axis normal to said predetermined axis, a radio receiver connected to said antenna, a rectifier connected to said receiver, means for reversing the polarity of the output of said rectifier periodically and in synchroni'sm with said alterations in the directivity of said antenna, a cathode ray tube including a fluorescent screen, means responsive to the angular position of said shaft to deflect the beam of said cathode ray tube radially outward from the center of said screen in a direction corresponding to said angular position, and means responsive to the output of said polarity-reversing means to control the extent of said radial deflection as a predetermined function of said output.

9.- A radio direction finder system including a directive antenna, means including a shaft for rotating said antenna about a verticalaxis, a radio receiver connected to said antenna, a rectifler connected to said radio receiver, a cathode ray tube including a fluorescent screen and cathode ray deflection means, means coupled to said shaft and responsive to the angular position thereof to deflect the cathode ray of said tube radiall outward from the center of said screen in a direction corresponding to said angular position, and means responsive to the output of said rectifier to control the extent of said radial deflection directly in accordance with the output of said rectifier, whereby rotation of said shaft causes a trace upon said screen conforming in shape to the directive pattern of said antenna and angularly positioned in accordance with the direction of arrival of a radio wave at said antenna.

EDWARD D. BLODGETT. DONALD S. BOND.

REFERENCES CITED The following references are of record in the file of this patent:

a UNITED STATES PATENTS Number Name Date 2,151,917 Hyland Mar. 28, 1939 2,263,377 Busignies et al. Nov. 18, 1941 2,295,412 Little Sept. 8, 1942 2,334,247 Busignies Nov. 16, 1943 FOREIGN PATENTS Number Country Date 635,793 Germany Sept. 28, 1936 

